Linear alpha-olefin is an important substance used in comonomers, detergents, lubricants, plasticizers, and the like, and is widely used commercially. In particular, 1-hexene and 1-octene are widely used as comonomers for controlling the density of polyethylene when manufacturing linear low density polyethylene (LLDPE).
Linear alpha-olefins such as 1-hexene and 1-octene are typically prepared through an oligomerization reaction of ethylene. The ethylene oligomerization reaction is performed through an oligomerization reaction (trimerization or tetramerization) of ethylene using ethylene as a reactant, and the product produced through the reaction contains not only a multicomponent hydrocarbon mixture including the desired 1-hexene and 1-octene, but also unreacted ethylene. The product undergoes a separation process in a distillation column, during which unreacted ethylene is recovered and reused in the ethylene oligomerization reaction.
Hereinafter, typical process methods will be described with reference to FIGS. 1 and 2.
As illustrated in FIG. 1, a typical process for recovering unreacted ethylene is performed through a process system which includes a distillation column 200, a condenser 63, a reflux drum 80, and a reboiler 73. For example, ethylene oligomerization reactant is supplied to the distillation column 200 through a reactant supply line 10, and the relatively ethylene-rich top fraction is condensed by being transported to the condenser 63 through a top discharge line 60, and is then introduced into the reflux drum 80. Liquid phase components of the top fraction in the reflux drum 80 are reintroduced into the distillation column 200 through a first reflux line and gas phase components are discharged through a first recovery line 62. Moreover, a bottom fraction containing 1-hexene and 1-octene is introduced into the reboiler 73, and then vaporized and reintroduced into the distillation column through a second reflux line 71 or discharged through a second recovery line 72.
In addition, as illustrated in FIG. 2, a typical process for recovering unreacted ethylene is performed through a process system which includes a first flashing column 100, a distillation column 200, a condenser 63, a reflux drum 80, and a reboiler 73. For example, an ethylene oligomerization reactant is supplied to a first flashing column 100 through a supply line 10, a relatively ethylene-rich top fraction is recovered after being discharged through a first top discharge line 30, and a bottom fraction containing residual ethylene is supplied to the distillation column 200 through a first bottom discharge line 40. Next, the relatively ethylene-rich top fraction is condensed after being transported to the condenser 63 through a second top discharge line 60, and is then introduced into the reflux drum 80. The liquid phase components of the top fraction in the reflux drum 80 are reintroduced into the distillation column 200 through a first reflux line 61, and the gas phase components are discharged through a first recovery line 62. A bottom fraction containing 1-hexene and 1-octene is introduced into the reboiler 73 through a second bottom discharge line 70, and then vaporized and reintroduced into the distillation column 200 through a second reflux line 71 or discharged through a second recovery line 72.
Typical methods such as above necessarily use a large amount of a cooling medium during the process of condensing and refluxing ethylene due to the low boiling point of ethylene (about −103.7° C.), and the cooling medium is costly. Thus, there is a limitation of poor economic efficiency.
Therefore, there is a demand for an economically efficient method for recovering ethylene from an ethylene oligomerization reactant, in which unreacted ethylene may be easily separated and recovered.